This invention deals with the determination of sulfur and carbon in fluids. More particularly, materials, methods and articles have now been discovered which permit the electrochemical determination of sulfur or carbon in diverse fluids, especially in melts. Even more particularly, means have now been discovered for the measurement of the concentration of sulfur or carbon in molten metals such as in molten copper and steel. It is believed that electrochemical cell measurement of sulfur or carbon in fluids has heretofore been impossible.
Electrochemicals sensors adapted for the measurement of oxygen in liquids such as in metallurgical melts are known. See in this regard "Developing New Electrochemical Sensors," Worrell, Proceedings of the Symposium on Metal-Slag-Gas Reaction and Processes, Electrochemical Society, Princeton (1975); "Oxide Solid Electrolytes," Worrell, Topics in Applied Physics, Geller Ed., Springer (1977); and "The Measurement of Oxygen Chemical Potentials for the Calcium Fluoride Solid Electrolyte," Worrell et.al., Journal of the Electrochemical Society, Vol. 126, No. 8, pp. 1360-1363 (1979). The foregoing references are incorporated herein by reference in order to describe more fully the electrochemical determination of elemental compositions employing solid electrolyte sensors. The foregoing publications disclose the employment of certain simple solid solutions such as those of zirconium oxide and thorium oxide in the electrochemical detection of oxygen. Electrolytes suitable for the electrochemical measurement of sulfur or carbon under laboratory conditions have been disclosed. Calcium fluoride, for example, has been proposed for such use. See "The Measurement of Sulfur Chemical Potential Differences Using a Calcium Fluoride Solid Electrolyte," Worrell et.al., Journal of the Electrochemical Society: Electrochemical Science and Technology, pp. 1717-1721, August 1980; and "Galvanic-Cell Investigation With a CaF.sub.2 Solid Electrolyte at Elevated Temperatures," Worrell, Solid State Ionics 3/4, pp. 559-563 (1981). Further attempts at the electrochemical measurement of sulfur have been reported. Thus, the employment of calcium-sulfide-based electrolytes is reported in "Development of the High-Temperature Solid-Sulfide Electrolyte," Worrell et.al., High Temperature Technology, IUPAC, pp. 503-509 (1969). Employment of barium carbide-barium fluoride solutions for measurement of carbon has also been reported. Each of the foregoing methods and materials proposed for the measurement of sulfur or carbon in electrochemical cells has met with severe practical limitations. For example, calcium fluoride-based electrolytes, such as calcium fluoride-calcium sulfide can be used successfully to measure sulfur potentials at temperatures between 500.degree. and 950.degree. C., however such electrolytes will not function in oxidizing environments "presumably due to the formation of an oxide coating." See the solid State Ionics article referred to above.
Other systems for the measurements of sulfur including CaS(Y.sub.2 S.sub.3), K.sub.2 SO.sub.4, Na.sub.2 SO.sub.4, Na.sub.2 SO.sub.4 (5% Ag.sub.2 SO.sub.4) and others have been studied. Each of those proposed suffer from drawbacks such as instability to oxygen and/or water or disproportionation in the presence of high sulfur concentration. At the present time, no electrochemical cell system for the determination of sulfur or carbon in fluids is known.